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Date: Mon, 28 Oct 2019 13:42:43 +0000
From: Robin Murphy <robin.murphy@....com>
To: Laurentiu Tudor <laurentiu.tudor@....com>,
"hch@....de" <hch@....de>, "joro@...tes.org" <joro@...tes.org>,
Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
Ioana Ciornei <ioana.ciornei@....com>
Cc: Leo Li <leoyang.li@....com>,
Diana Madalina Craciun <diana.craciun@....com>,
"davem@...emloft.net" <davem@...emloft.net>,
Madalin Bucur <madalin.bucur@....com>
Subject: Re: [PATCH v2 1/3] dma-mapping: introduce new dma unmap and sync api
variants
On 24/10/2019 13:41, Laurentiu Tudor wrote:
> From: Laurentiu Tudor <laurentiu.tudor@....com>
>
> Introduce a few new dma unmap and sync variants that, on top of the
> original variants, return the virtual address corresponding to the
> input dma address.
> In order to implement this a new dma map op is added and used:
> void *get_virt_addr(dev, dma_handle);
> It does the actual conversion of an input dma address to the output
> virtual address.
At this point, I think it might be better to just change the prototype
of the .unmap_page/.sync_single_for_cpu callbacks themselves. In cases
where .get_virt_addr would be non-trivial, it's most likely duplicating
work that the relevant callback has to do anyway (i.e. where the virtual
and/or physical address is needed internally for a cache maintenance or
bounce buffer operation). It would also help avoid any possible
ambiguity about whether .get_virt_addr returns the VA corresponding
dma_handle (if one exists) rather than the VA of the buffer *mapped to*
dma_handle, which for a bounce-buffering implementation would be
different, and the one you actually need - a naive
phys_to_virt(dma_to_phys(dma_handle)) would lead you to the wrong place
(in fact it looks like DPAA2 would currently go wrong with
"swiotlb=force" and the SMMU disabled or in passthrough).
One question there is whether we'd want careful special-casing to avoid
introducing overhead where unmap/sync are currently complete no-ops, or
whether an extra phys_to_virt() or so in those paths would be tolerable.
> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@....com>
> ---
> include/linux/dma-mapping.h | 55 +++++++++++++++++++++++++++++++++++++
> 1 file changed, 55 insertions(+)
>
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 4a1c4fca475a..ae7bb8a84b9d 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -132,6 +132,7 @@ struct dma_map_ops {
> u64 (*get_required_mask)(struct device *dev);
> size_t (*max_mapping_size)(struct device *dev);
> unsigned long (*get_merge_boundary)(struct device *dev);
> + void *(*get_virt_addr)(struct device *dev, dma_addr_t dma_handle);
> };
>
> #define DMA_MAPPING_ERROR (~(dma_addr_t)0)
> @@ -304,6 +305,21 @@ static inline void dma_unmap_page_attrs(struct device *dev, dma_addr_t addr,
> debug_dma_unmap_page(dev, addr, size, dir);
> }
>
> +static inline struct page *
> +dma_unmap_page_attrs_desc(struct device *dev, dma_addr_t addr, size_t size,
> + enum dma_data_direction dir, unsigned long attrs)
> +{
> + const struct dma_map_ops *ops = get_dma_ops(dev);
> + void *ptr = NULL;
> +
> + if (ops && ops->get_virt_addr)
> + ptr = ops->get_virt_addr(dev, addr);
Note that this doesn't work for dma-direct, but for the sake of arm64 at
least it almost certainly wants to.
Robin.
> + dma_unmap_page_attrs(dev, addr, size, dir, attrs);
> +
> + return ptr ? virt_to_page(ptr) : NULL;
> +}
> +
> /*
> * dma_maps_sg_attrs returns 0 on error and > 0 on success.
> * It should never return a value < 0.
> @@ -390,6 +406,21 @@ static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
> debug_dma_sync_single_for_cpu(dev, addr, size, dir);
> }
>
> +static inline void *
> +dma_sync_single_for_cpu_desc(struct device *dev, dma_addr_t addr, size_t size,
> + enum dma_data_direction dir)
> +{
> + const struct dma_map_ops *ops = get_dma_ops(dev);
> + void *ptr = NULL;
> +
> + if (ops && ops->get_virt_addr)
> + ptr = ops->get_virt_addr(dev, addr);
> +
> + dma_sync_single_for_cpu(dev, addr, size, dir);
> +
> + return ptr;
> +}
> +
> static inline void dma_sync_single_for_device(struct device *dev,
> dma_addr_t addr, size_t size,
> enum dma_data_direction dir)
> @@ -500,6 +531,12 @@ static inline void dma_sync_single_for_cpu(struct device *dev, dma_addr_t addr,
> size_t size, enum dma_data_direction dir)
> {
> }
> +
> +static inline void *
> +dma_sync_single_for_cpu_desc(struct device *dev, dma_addr_t addr, size_t size,
> + enum dma_data_direction dir)
> +{
> +}
> static inline void dma_sync_single_for_device(struct device *dev,
> dma_addr_t addr, size_t size, enum dma_data_direction dir)
> {
> @@ -594,6 +631,21 @@ static inline void dma_unmap_single_attrs(struct device *dev, dma_addr_t addr,
> return dma_unmap_page_attrs(dev, addr, size, dir, attrs);
> }
>
> +static inline void *
> +dma_unmap_single_attrs_desc(struct device *dev, dma_addr_t addr, size_t size,
> + enum dma_data_direction dir, unsigned long attrs)
> +{
> + const struct dma_map_ops *ops = get_dma_ops(dev);
> + void *ptr = NULL;
> +
> + if (ops && ops->get_virt_addr)
> + ptr = ops->get_virt_addr(dev, addr);
> +
> + dma_unmap_single_attrs(dev, addr, size, dir, attrs);
> +
> + return ptr;
> +}
> +
> static inline void dma_sync_single_range_for_cpu(struct device *dev,
> dma_addr_t addr, unsigned long offset, size_t size,
> enum dma_data_direction dir)
> @@ -610,10 +662,13 @@ static inline void dma_sync_single_range_for_device(struct device *dev,
>
> #define dma_map_single(d, a, s, r) dma_map_single_attrs(d, a, s, r, 0)
> #define dma_unmap_single(d, a, s, r) dma_unmap_single_attrs(d, a, s, r, 0)
> +#define dma_unmap_single_desc(d, a, s, r) \
> + dma_unmap_single_attrs_desc(d, a, s, r, 0)
> #define dma_map_sg(d, s, n, r) dma_map_sg_attrs(d, s, n, r, 0)
> #define dma_unmap_sg(d, s, n, r) dma_unmap_sg_attrs(d, s, n, r, 0)
> #define dma_map_page(d, p, o, s, r) dma_map_page_attrs(d, p, o, s, r, 0)
> #define dma_unmap_page(d, a, s, r) dma_unmap_page_attrs(d, a, s, r, 0)
> +#define dma_unmap_page_desc(d, a, s, r) dma_unmap_page_attrs_desc(d, a, s, r, 0)
> #define dma_get_sgtable(d, t, v, h, s) dma_get_sgtable_attrs(d, t, v, h, s, 0)
> #define dma_mmap_coherent(d, v, c, h, s) dma_mmap_attrs(d, v, c, h, s, 0)
>
>
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